Lost Nuke Knowledge: the Decline of Western Civilization?

This is odd:

PLANS TO refurbish Trident nuclear weapons had to be put on hold because US scientists forgot how to manufacture a component of the warhead, a US congressional investigation has revealed.

The US National Nuclear Security Administration (NNSA) "lost knowledge" of how to make a mysterious but very hazardous material codenamed Fogbank. As a result, the warhead refurbishment programme was put back by at least a year, and racked up an extra $69 million.

According to some critics, the delay could cause major problems for the UK Trident programme, which is very closely tied to the US programme and uses much of the same technology. The US and the UK are trying to refurbish the ageing W76 warheads that tip Trident missiles in order to prolong their life, and ensure they are safe and reliable. This apparently requires that the Fogbank in the warheads is replaced.

Neither the NNSA nor the UK Ministry of Defence would say anything about the nature or function of Fogbank. But it is thought by some weapons experts to be a foam used between the fission and fusion stages of a thermonuclear bomb. US officials have said that manufacturing the material requires a solvent cleaning agent which is "extremely flammable" and "explosive". The process also involves dealing with "toxic materials" hazardous to workers.

Note the close tie between the US and UK nuke program...

In a way, it's good that we have lost this particular expertise -- though I'm sure we have newer ways of making nukes. It's just very odd to me that we "lost" this particular knowledge.. very curious-- I wonder if there is more to this story...